The present invention relates to syringes fillable with a liquid agent for use as attached to injectors for medical procedures, such as angiography, computerized tomography, NMR/MRI, etc., to be performed with a contrast medium, chemical agent or like liquid agent injected into the vascular system of the human body or an animal.
As disclosed in U.S. Pat. No. 4,006,736, syringes for use in examining patients in medical procedures are used by attaching the main body of the syringe to an injector and fixing a plunger fitted in the syringe body in intimate contact therewith to a piston of the injector. The piston advances at a speed controlled by a control circuit of the injector, pushing the plunger to inject a liquid agent filled in the syringe into the vascular system of the patient.
Further, U.S. Pat. No. 4,677,980 discloses a syringe including a plunger which is connectable to a piston or disconnectable therefrom by rotating the entire syringe through about 90 deg relative to the piston, with the plunger held in contact with the forward end of the piston.
Further International Publication No. WO 98/20920 (corresponding to Japanese Patent Application No. 522638/1998) discloses a syringe 2 shown in FIGS. 10 and 11.
The syringe 2 comprises a cylindrical syringe body 3 and a plunger 4 fitted in the syringe body. The syringe 2 is connected to an injector 1 by removably fixing a base end of the syringe body 3 in a syringe socket 11 of the injector 1 and releasably engaging the plunger 4 of the syringe 2 with a piston 13 which is movable out of or into the socket 11 centrally thereof. The piston 13 is projected outward at a controlled speed by a drive device (not shown) incorporated in the injector 1, thereby advancing the plunger 4 toward the forward end of the syringe body 3 to inject a liquid agent filled in the syringe body 3 into the vascular system of the human body or an animal through a tube (not shown) from a nozzle 30 at the front end of the syringe body 3.
In the following description, the term xe2x80x9cfrontxe2x80x9d or xe2x80x9cforwardxe2x80x9d refers to one side of the syringe 2 where the syringe body 3 is connected to the patient and the liquid agent is forced out by the plunger 4, and the term xe2x80x9crearxe2x80x9d or xe2x80x9crearwardxe2x80x9d refers to the other side opposite to the above side where the syringe is connected to the injector.
The inner periphery of the socket 11 of the injector 1 is provided with syringe holding flanges 12, 12. Projecting from the syringe body 3 radially thereof are ridges 31 engageable with the flanges 12, 12 and a flange 32 adapted for bearing contact with the end face of the socket 11.
The piston 13 is provided at its front end with plunger holding pieces 14, 14 orthogonal to the axis of the piston 13.
With reference to FIG. 13, the plunger 4 disclosed in the foregoing publication WO No. 98/20920 comprises a plunger body 5 and an elastic cover 9 fitted over the body 5.
The plunger body 5 comprises two members which are fitted together, i.e., a conical portion 81 at the front end, and a hollow truncated cone 82 fitted to the conical portion 81, extending rearward and having a gently tapered conical surface.
A circular backplate 62 extends from the rear end of the truncated cone 82 radially thereof, with a recessed portion 52 formed between the backplate 62 and the cone 82 over the entire circumference thereof.
Projecting rearward from the rear end of the conical portion 81 are a pair of connecting legs 71, 71 each having an inward claw 76.
The elastic cover 9 is fitted over the plunger body 5 to extend over the conical portion 81 thereof to the recessed portion 52, and comprises a hollow conical portion 91, a cylindrical portion 92 extending from the conical portion 91, an inward flange 94 projecting from the rear end of the cylindrical portion 92 and a projection 96 extending forward from the front end of the conical portion 91. A plurality of ribs 93, 93 are formed on the outer peripheral surface of the cylindrical portion 92 over the entire circumference thereof.
The projection 96 is positioned in the tubular nozzle 30 at the front end of the syringe body 3 on completion of advance of the plunger 4, minimizing the quantity of the liquid agent remaining within the syringe body 3 and to be wasted.
The hollow conical portion 91 of the elastic cover 9 covers the conical portion 81 of the plunger body 5 with a small space 90 left therebetween. The cylindrical portion 92 covers the truncated cone 82 in intimate contact therewith, with the inward flange 94 fitting in the recessed portion 52 around the cone 82.
The syringe body 3 is fitted at its base end into the socket 11 of the injector 1 and then rotated through about 90 deg to position the ridge 31 of the syringe body 3 inside the syringe holding flange 12 formed on the inner surface of the socket 11, whereby the syringe body 3 is prevented from slipping out of the socket 11.
The piston 13 of the injector 1 as retracted is positioned away from the plunger 4 of the syringe 2. When the piston 13 is projected outward gradually, however, the holding pieces 14, 14 at the front end of the piston force the pair of legs 71, 71, projecting from the rear side of the plunger 4, away from each other and are brought into engagement with the claws 76, 76 at the front side thereof (see FIG. 13). Since the front end face of the piston 13 comes into pushing contact with the plunger body 3, the plunger 4 advances, whereby the liquid agent in the syringe 2 is injected into the vascular system of the human body or animal as described above.
To remove the syringe 2 from the injector 1 after it is used for injecting the liquid agent, the syringe body 3 is rotated through about 90 deg in a direction opposite to the direction in which the body is rotated for connection. This releases the ridge 31 of the syringe body 3 from engagement with the syringe holding flange 12 of the injector socket 11 and the claws 76, 76 of the plunger 4 from engagement with the holding pieces 14, 14 of the piston 13. The syringe 2 is removed from the socket 11.
The syringe 2 shown in FIG. 11 and described above needs to be so designed as to withstand the pressure of injecting the liquid agent. As shown in FIG. 12, such a syringe 2 is also used as sheathed in a reinforcing case 200 on a turret 100 for connection to an injector 1.
Like the foregoing one, this type of syringe 2 comprises a syringe body 3 and a plunger 4, whereas the syringe body 3 need not withstand the internal pressure involved in injecting the liquid agent but has characteristics to slightly expand under the internal pressure.
The syringe body 3 is provided at its rear end with parallel flanges 36, 36 each having a cut portion 37 for preventing rotation. The syringe 2 is removably fitted into the case or pressure jacket 200 supported by the turret 100 and is set in position.
The turret 100 has stepped through bores 101, 101 at opposite sides of a hole 102 which provides the center of rotation of the turret 100.
Tubular transparent reinforcing cases or pressure jackets 200, 200 are inserted from behind the turret 100 through the respective bores 101, 101 in the turret 100.
The reinforcing case 200 has a rear end provided with a flange 201 serving as a retainer and a front end tapered in the form of a cone and formed with a hole 202 for a nozzle 30 of the syringe body 3 to extend therethrough.
The injector 1 is provided with a turret rotating support pin 16 above a piston 13 and a turret receiving portion 18 below the piston 13.
The syringe 2 is inserted into one of the reinforcing cases 200 on the turret 100, the support pin 16 is fitted into the hole 102 in the turret 100, the forward end of a screw 104 driven into the turret 100 orthogonally to the hole 102 is fitted into a groove 17 in the support pin 16, and one end of the turret 100 is engaged with the receiving portion 18 projecting from the injector 1 to prevent the turret 100 from slipping off.
When the piston 13 is connected to the plunger 4 of the syringe 2 as inserted in the case 200, with the axis of the case 200 on the turret 100 aligned with the axis of the piston 13, another syringe 2 can be inserted into or removed from the other case 200.
The syringe body 3 is expanded into intimate contact with the inner surface of the reinforcing case 200 by the internal pressure acting on the syringe body 3 when the liquid agent in the syringe 2 is injected by the advancement of the piston 13. The syringe body 3 withstands the internal pressure of injection by virtue of the strength of the case or pressure jacket 200.
In the case of the syringe 2 shown in FIGS. 11 and 12 and described above, the cylindrical portion 92 of the elastic cover 9 fitting around the truncated cone 82 of the plunger body 5 is brought into intensely frictional contact with the inner surface of the syringe body 3 when the plunger 4 advances as shown in FIG. 13, with the result that the conical portion 91 of the cover stretches toward a rearwardly tapered region between the inner surface of the syringe body 3 and the truncated portion 82 of the plunger body 5, producing an effect achieved as by forcing in a wedge (hereinafter referred to as a xe2x80x9cwedging effectxe2x80x9d). The elastic material in this region is compressed to a higher degree, making it possible to inject the liquid agent within the syringe body 3 into the vascular system of the human body or animal at a higher pressure than conventionally. Accordingly, the liquid agent can be injected into arterial vessels at a pressure higher than arterial blood pressure.
However, higher pressures impose limitations on the operation of the syringe 2 although it is adapted for high-pressure injection.
When the internal pressure of the syringe 2 is increased by the advance of the plunger 4, an enhanced wedging effect presses the elastic cover 9 against the inner surface of the syringe body 3 with a greater force, whereby the cylindrical portion 92 of the cover 9 is compressed under higher pressure and becomes seriously impaired in slipperiness.
The elastic cover 9 is stretched further rearward by the advance of the piston 13, but blocked by the backplate 62 and forced into a minute clearance between the periphery of the backplate 62 and the inner surface of the syringe body 3. This entails the problem that the portion of the cover 9 forced in has its surface scraped off in a very small amount by pressing contact with the syringe body 3, leaving scraped-off minute fragments on the syringe body inner surface during continued injection. Furthermore, the elastic cover 9 thus forced in offers excessive resistance to the advancement of the plunger 4.
In view of the foregoing problems, the present invention provides a syringe which is usable for high-pressure injection without permitting an elastic plunger cover to release scraped-off minute fragments thereof into the syringe while allowing the plunger to advance therein.
The present invention provides a medical syringe 2 comprising a cylindrical syringe body 3 and a plunger 4 fitted in the syringe body 3 for injecting a liquid agent filled in the syringe body 3 from the syringe body 3 into the vascular system of a human body or animal by advancing the plunger 4 relative to the syringe body 3, the plunger 4 comprising a plunger body 5 and an elastic cover 9 fitted over the plunger body 5 from the front, the plunger body 5 being provided with a backplate 62 at a rear end thereof, the backplate 62 having an annular groove 68 forwardly opened and formed in a front surface thereof in the vicinity of an outer periphery thereof.
When the plunger 4 is pushed under high pressure against arterial blood pressure, the elastic cover 9 over the plunger body 5 stretches rearward in sliding contact therewith and is forced in between the plunger body 5 and the inner surface of the syringe body 3 and thereby compressed to a higher degree to produce an enhanced sealing effect. Although the rear end of the elastic cover 9 is stretched rearward by the advance of the plunger 4, the stretched portion is allowed to escape into the annular groove 68 forwardly opened and formed in the front surface outer peripheral portion of the backplate 62.
An outer annular wall 68c defining the annular groove 68 serves to guide the outer periphery of the rearwardly stretched portion of the elastic cover 9 toward the annular groove 68.
This eliminates the conventional likelihood that the rearwardly stretched cover portion will wedge into the very small clearance between the outer periphery of the backplate 62 and the inner surface of the syringe body 3 during the advance of the plunger 4, producing minute scraped-off fragments and causing troubles such as the failure of the plunger 4 to advance.
The base end of the elastic cover 9 escaping into the annular groove 68 fills up the groove 68, pressing the inner surface of the syringe body 3 to achieve a further improved sealing effect.
The liquid agent within the syringe body 3 can be injected into the vascular system of the human body or animal with an exceedingly higher pressure than is the case with the syringe 2 disclosed in International Publication No. WO98/20920 described, by virtue of the function of the annular groove 68 of the plunger 4. A high pressure is available in the range of 87 kg/cm2 to 98 kg/cm2 without entailing problems such as the release of scraped-off fragments of the elastic cover 9 of the plunger 4 and the failure of the plunger 4 to advance.
When the rear end face of the elastic cover 9 is formed with an annular ridge 95 concentric with the cover, the ridge 95 can easily escape into the annular groove 68 when the rear end of the elastic cover 9 is stretched rearward by the advance of the plunger 4.
When the plunger body 5 has a recessed portion 52 formed in the periphery of a rear portion thereof and continuous with the opening of the annular groove 58 of the backplate 62, the elastic cover 9 can be prevented from slipping off the plunger body 5 by fitting an inward flange 94 formed on the inner surface of the elastic cover 9 into the recessed portion 52, before the plunger body 5 is fitted into the syringe body 3 in the assembling step.
When the annular groove 68 formed in the front surface of the backplate 62 is so shaped in cross section that opposite side faces defining the groove 68 are inclined or curved toward each other to give the groove a width decreasing toward its bottom, the backplate 62 can be given an increased strength without giving an increased thickness to the groove-defining walls of the backplate.
Further when the annular groove 68 is shaped in conformity with the shape of the annular ridge 95 at the rear end of the elastic cover 9 in cross section, the inclination of the groove-defining side faces 68a, 68b enables the annular ridge 95 to ingress into the groove 68 for escape with greater ease.
It is desired to mold the elastic cover 9 from a composition which has incorporated therein a material, such as paraffin wax or polyethylene, having solid lubricity, or a composition which has incorporated therein a superfine speherical lubricating component of polyethylene, nylon, Teflon or like synthetic resin. The elastic cover 9 is then slidable on the inner surface of the syringe body 3 with improved smoothness to reduce the resistance to the injection by the plunger.